When two wireless terminals (e.g., UEs or mobile communication devices) of a cellular network or other telecommunication system communicate with each other, their data path has historically gone through the operator network. The data path through the network may include base stations and/or gateways. If the wireless terminals are in close proximity with each other, their data path may be routed locally through a local base station. In general, communications between a network node such as a base station and a wireless terminal is known as “WAN” or “Cellular communication”.
It is also possible for two wireless terminals in close proximity to each other to establish a link with one another without the need to go through a base station. Telecommunications systems may use or enable such device-to-device (“D2D”) communication, in which two or more user equipment terminals communicate with one another. In D2D communication, voice and data traffic (referred to herein as “communication signals”) from one user equipment terminal may be transmitted to one or more other user equipment terminals may without the communication signals passing through a base station or other network control device of a telecommunication system. As such, device-to-device (D2D) communications differ from “WAN” or “Cellular communication”. Device-to-device (D2D) communication has more recently also become known as “sidelink direct communication”.
Sidelink direct communication may be used in networks implemented according to any suitable telecommunications standard. A non-limiting example of such as standard is the 3rd Generation Partnership Project (“3GPP”) Long Term Evolution (“LTE”). The 3GPP standard is a collaboration agreement that aims to define globally applicable technical specifications and technical reports for present and future generation wireless communication systems. The 3GPP may define specifications for next generation mobile networks, systems, and devices. The 3GPP LTE is the name given to a project to improve the Universal Mobile Telecommunications System (“UMTS”) mobile phone or device standard to cope with future requirements. In one aspect, UMTS has been modified to provide support and specification for the Evolved Universal Terrestrial Radio Access (“E-UTRA”) and Evolved Universal Terrestrial Radio Access Network (“E-UTRAN”). E-UTRAN is another non-limiting example of a telecommunications standard with which D2D communication may be used.
A non-exhaustive list of 3GPP documents which describe, at least in part, device-to-device (D2D) communication (e.g., “sidelink direct communication”), and which may be pertinent to the technology disclosed herein, include the following (all of which are incorporated herein by reference in their entireties):                R2-150645, 3GPP TSG-RAN WG2 Meeting #89, Athens, Greece, Feb. 9-13, 2015, Corrections to Stage 2 Description of ProSe (“R2-150645”).        R1-150962, Introduction of D2D (ProSe) feature into 3GPP TS 36.213 V12.4.0 (2014-December), (“R1-150962”).        R2-150734, 3GPP TSG-RAN2#89 meeting Athens, Greece, 9-13 Feb. 2015, change request to 36.331 V. 14.4.1 (“R2-150734”).        3GPP TS 23.303 V12.4.0 (2015-March), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures; (Release 12).        3GPP TS 36.843 V12.0.1 (2014-March), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Study on LTE Device to Device Proximity Services; Radio Aspects.        
R2-150645 §23.10.3 describes, e.g., radio resource allocation for Proximity Service, and in particular two modes of resource allocation known as the scheduled resource allocation mode and the autonomous resource selection mode. As described in §23.10.3, scheduled resource allocation is characterized by the wireless terminal (UE) being RRC_CONNECTED mode in order to transmit data, and the wireless terminal (UE) requesting transmission resources from the eNodeB (after which the eNB schedules transmission resources for transmission of Sidelink Control and data). On the other hand, UE autonomous resource selection is characterized by a UE on its own selecting resources from resource pools and performing transport format selection to transmit Sidelink Control and data.
R2-150645 §23.10.3 further describes, e.g., that a UE is considered in-coverage for ProSe Direct Communication whenever it detects a cell on a Public Safety ProSe Carrier in accordance with specified criteria. R2-150645 §23.10.3 also discusses resource selection/allocation rules; what happens when a UE that is camped or connected to one carrier frequency but interested in ProSe Direct Communication in another carrier frequency; and certain selection options for a cell on the Public Safety ProSe carrier.
R2-150645 §23.10.3.1 describes, e.g., resource pools for sidelink control, both for when a wireless terminal is out-of-coverage and within coverage. For an out-of-coverage UE, the resources pools used for reception and transmission are pre-configured. For an in coverage UE, the reception resource pool and the transmission resource pool are configured by the eNodeB. R2-150645 §23.10.3.2 describes, e.g., resource pools for sidelink data.
R2-150645 §23.10.3.1 describes, e.g., support for ProSe Direct Discovery. ProSe Direct Discovery is a procedure used by the UE to discover other wireless terminals (e.g., UEs) in its proximity, using E-UTRA direct radio signals via the PC5 interface. ProSe Direct Discovery is only supported when the UE is served by E-UTRAN. R2-150645 §23.10.3.1 explains, e.g., that an upper layer (e.g., ProSe Protocol) handles authorization for announcement and monitoring of discovery messages. The ProSe Protocol layer is above the medium access control (MAC) layer, which in turn is above the physical layer. Such is also described in R2-150645 §23.11.2, which pertains to radio protocol architecture.
R2-150645 §23.11.3 describes, e.g., two types of resource allocation for a discovery message announcement (UE autonomous resource selection and scheduled resource allocation) and characteristics of both types of resource allocation.
R2-150645 §23.11.3 also states that, for UEs in RRC_IDLE, the eNodeB may selection one of two options. The first option is that the eNB may provide a resource pool for UE autonomous resource selection based discovery message announcement in system information block (SIB 19), and UEs that are authorized for Prose Direct Discovery use these resources for announcing discovery message in RRC_IDLE. The second option is that the eNB may indicate in SIB 19 that it supports ProSe Direct Discovery but does not provide resources for discovery message announcement, in which case the UEs need to enter RRC_CONNECTED in order to request resources for discovery message announcement.
R2-150645 §23.11.3 also states, e.g., that for UEs in RRC_CONNECTED, the eNB may configure the UE with a resource pool for UE autonomous resource selection for discovery message announcement via dedicated signaling. The resources allocated by the eNB via dedicated signalling are valid until the eNB re-configures the resource(s) by RRC signalling or the UE enters RRC_IDLE. Authorized receiving UEs in RRC_IDLE and RRC_CONNECTED may monitor resource pools used for UE autonomous resource selection and resource pools for scheduled resource allocation. The eNB provides the resource pool configuration used for discovery message monitoring in SIB 19. The SIB 19 may contain detailed ProSe Direct Discovery configuration used for announcing in neighbour cells of intra-frequency as well.
R2-150645 §23.11.3 further states, e.g., that a UE if authorized by the network (NW) can announce discovery message only on a serving cell. The UE can monitor discovery resources in the same as well as other frequencies than the serving cell, in same or different PLMNs. The serving cell may provide in SIB 19 a list of frequencies along with PLMN ID on which the UE may aim to monitor discovery message. An RRC_CONNECTED UE sends a ProSe UE Information indication to the serving cell if it is interested or no longer interested in intra-frequency, inter-frequency or inter-PLMN discovery message monitoring.
R1-150962 describes, e.g., physical sidelink discovery channel procedures. Among the procedures described are a UE procedure for transmitting the PSDCH (§14.3.1); a UE procedure for receiving the PSDCH (§14.3.2); and a UE procedure for determining resource block pool and subframe pool for sidelink discovery (§14.3.3).
R2-150734 describes, e.g., certain ProSe discovery related information, such as actions upon reception of SystemInformationBlockType19 (§5.2.2.x2); conditions for establishing RRC connection for sidelink direct communication/discovery (§5.3.3.1a), and sidelink dedicated configuration (§5.3.10x). In addition, R2-150734 provides, e.g., an introduction to sidelink (§5.x et seq), including conditions for sidelink operation and sidelink UE information (initiation, actions related to transmission of SidelinkUEInformation message, direct discovery monitoring, and direct discovery announcement), as well as sidelink pre-configured parameters (§9.x).
3GPP TS 23.303 V12.4.0 (2015-March) provides an overview of ProSe Direct Discovery (§5.3.1.1), including ProSe Direct Discovery Models A and B.
Generally, there are three scenarios which may occur in sidelink discovery. Those three sidelink direct discovery scenarios are illustrated in FIG. 1. A first of the sidelink discovery scenario is an “in coverage” discovery scenario, illustrated as SL discovery between UE1 and UE2 of FIG. 1, in which both UE1 and UE2 are within coverage of the radio access network. A second sidelink discovery scenario is a “partial coverage” discovery scenario, illustrated as SL discovery between UE2 and UE3 of FIG. 1. In the “partial coverage” sidelink discovery scenario the wireless terminal UE2 is within coverage of the radio access network, but the wireless terminal UE3 is out-of-coverage of the radio access network. A third sidelink discovery scenario is an “out-of-coverage” discovery scenario, illustrated as SL discovery between wireless terminal UE3 and wireless terminal UE4 of FIG. 1. In the out-of-coverage sidelink discovery scenario both the wireless terminal UE3 and the wireless terminal UE4 are out-of-coverage of the radio access network.
The three sidelink discovery scenarios are described with reference to whether or not a participating wireless terminals (e.g., UEs) are “in coverage” or “out-of-coverage” of one or more radio access networks (which may collectively be referred to as a “radio access network”). For sake of simplicity FIG. 1 depicts “coverage” as being with respect to an access node such as eNodeB which comprises a radio access network. It should be understood, however, that a wireless terminal may also be in coverage of the radio access network when served by any cell of the radio access network(s). For example, If wireless terminal UE1 and wireless terminal UE2 were served by different cells, when participating in sidelink direct discovery the wireless terminal UE1 and wireless terminal UE2 would still be in an in coverage sidelink discovery scenario.
In 3GPP Release 12 proximity service (ProSe) specifications, two types of sidelink (SL) services were defined: SL communications and SL direct discovery. Sidelink communications cover in coverage (IC) and out of coverage (OOC) scenarios with corresponding resource pool allocation methods. However, SL direct discovery has been defined in 3GPP Release 12 only for the in coverage discovery scenario.
What is needed, therefore, and an example object of the technology disclosed herein, are methods, apparatus, and techniques for performing sidelink direct discovery in the partial coverage discovery scenario and the out-of-coverage discovery scenario.